Sunday, June 1, 2014

Green roofs in Florida must be designed for a very unique set of rooftop variables. Time and time again I see marvelous, well designed growing systems that work most everywhere else in the U.S. fail in Florida.

The first failure. Check out the sprinkler erosion patterns in the green roof soil media.

Beware. A successful Florida green roof is usually based not on the growing system. Successful Florida Green Roofs are all about the rooftop plant design. Other than hurricane resiliency and wind uplift issues, the green roof growing system could be a simple vertical coquina stone wall and with the right plants, be green and beautiful year around.

Remnants of the sedum plants that once covered the roof. More irrigation erosions visible in the soil media.

I do not understand why this concept is so hard to understand by some. But hopefully we can all learn from these 'hard' lessons.

Sedums work great north of Atlanta generally speaking. The black death fungus commonly known as Southern Blight, Sclerotium rolfsii, that is pervasively present here in the Sunshine State, apparently wiped out the entire rooftop planting in a matter of weeks.

Here in Florida there are a few 'constants' in green roofing design. The underlying roofing assembly should keep the building water tight. The entire roofing assembly and green roof system should be fire rated. Additionally, the roof and green roof growing system should be wind uplift and tropical storm resilient.

A coquina rock wall can satisfy most of these requirements. What I am trying to say is that here in Florida green roof plants can grow in any growing system installed on a roof.

What matters most is the type of plants chosen and how they interact with primary and secondary design variables.

The 10,000 square foot, green roof system shown here was a installed on the Aloft Hotel in Jacksonville, Florida by a well known national roofing company with a marvelous green roof line of products.

It has failed and failed and failed and was finally removed.

After the first attempt, perennial peanut, Arachis glabrata, was tried as a rooftop cover. This design too was a failure.

Such a waste of a beautiful green roof system.

Note the perimeter dead zone on the roof soon after the second round of plants were installed on the roof. Within a short time the perennial peanut took off, but so did the Bidens app, Goldenrod, Dog-fennel, Ragweed, Pokeberry and extremely tall 'weeds'.

Hoses were draped over the edge of the roof to supply lots of water to plants destined to failure from day one.

Whirly bird sprinklers were set up on the roof but in the end did not save the plants, rather they contributed to washing out the soil media and atomizing-spraying what smelled like reclaimed irrigation water all over the swimming pool and garden patio area below.

Hot summer, relentless photoactive radiation and no matter how much irrigation was applied the chosen plants dried up and turned brown.

This roof not only failed multiple times but also presented a serious liability and safety issue. With rooftop temperatures approaching 150 degrees F, an afternoon breeze laden with a single cigar ash could have turned the entire structure into a great big torch.

Sometimes a green roof designer will mistake 50 inch annual rainfall amounts for being spread evenly over four seasons. Here in Florida it is not uncommon to see ten, twelve or sixteen week droughts without a single drop of rain.

Again, the roof and growing system here are first class. But in Florida, a successful green roof is designed around the plants.

I recommend talking to a nursery specializing in green roof plants. Most nurseries know what drought tolerant plants to install on the ground, and the peanut might have worked well at the hotel site on the ground.

Yet, rooftop ecology needs are nowhere near the same as ground level landscape requirements. Leaf surface temperature differences can be as high as 80-90 degree F greater on the roof than on the ground. Find a green roof nursery specializing in green roof plants that has worked for years in your area.

Dead green roofs are fire hazards

Wind too can have so much more impact on the roof than on ground level. Perennial peanut's success on the ground is due to a hyper-fast photosynthesis rate and biomass creation. The plant grows fast and covers the ground quickly. However because the plant does not possess significant spatial or time based separation and protection of the Calvin Cycle processes, roof level heat and wind can pull the water out of the plant faster than the vascular system can resupply.

Maybe as soon as rains started the plant may have 'greened' up (possibly), yet during the dry periods an unacceptable and serious fire hazard existed.

The landscaper had previous success with peanut on the ground. But a Florida roof is unlike the ground.

Florida green roof design is all about the plants and not so much about the system.

Note too that because there is no handrail system, personal fall protection device attachments would have to be installed to protect maintenance workers.

Maintenance on a green roof should only be done by staff trained for working on a roof with personal fall protection equipment. Never allow a landscaper on a roof unless they are properly trained and equipped with safety gear, including a hardhat, safety glasses, high visibility vest and personal fall protection gear for starters.

But even with the proper maintenance procedures and awesome green roof planting bed, someone never figured out that it is 'all about the plants'.

The fort in St. Augustine, Castillo de San Marcos, is built with solid coquina rock walls, continually buffeted by strong salt laden winds and exposed to intense sunlight. But the walls support over fifty species of plants. No soil media and no added irrigation. Over time populations of native plants have made their self at home.

Castillo de San Marcos plant's teach us that here in Florida it is not so much about the rooftop growing system. It is not so much about the soil media, although the wrong soil media will not support long term growth. It is all about Right Plant Right Place on the green roof.

So if you want to design a Florida Green Roof you can learn via trial and failure over the years, or work with a plant person who understands rooftop ecology.

We are presenting a series of design articles covering the basics of rooftop plant design.

So follow our green roof modeling discussion on the Greenroofs.com website under their Tropical Green Roofs Section. Part one of the discussion was published a couple months ago. Part two of the design discussion is coming soon.

The green roof has been removed. What an amazing opportunity missed.

And for a quick revisit of the seven H's check out some of the other posts about designing Florida Green Roofs.

The green roof planting system installed above was really amazing. But forcing those plants though they may grow great elsewhere in the states, that are not suited for the 7H's, on a Florida green roof was not the right approach.

Then hiring a landscaper without a rooftop background to try and remedy the problem only magnified the issues leading to failure.

Thank goodness the landscapers did not fall off the roof. Thank goodness a cigarette ash did not land on the dead vegetation.

It is not really about the system. On a green roof, it is all about the plants.